Wambersie A, Menzel H G
Cliniques Universitaires St-Luc, Université Catholique de Louvain (UCL), Brussels, Belgium.
Bull Cancer Radiother. 1996;83 Suppl:68s-77s. doi: 10.1016/0924-4212(96)84888-2.
Fast neutrons were introduced in cancer therapy, in the 1970s, on the basis of radiobiological arguments. After 30 years, these arguments are still valid and have not been refuted by more recent experimental data. Although neutron therapy has been applied routinely for about 25 years, there is still no general agreement concerning its value and its place among the other radiation therapy techniques. In order to be able to draw objective conclusions from the available clinical results and mainly to compare the results from the different centres in a relevant way, a consensus has to be reached on several issues: 1) a protocol for dose measurement in a homogeneous phantom in reference conditions; 2) dose computation at the level of the target volume(s) and the normal tissues at risk; 3) method of dose specification for reporting; and 4) specification of radiation quality in neutron therapy and the related RBE problems. The International Commission on Radiation Units and Measurements (ICRU) has published recommendations on Clinical Neutron Dosimetry (ICRU Report 45, 1989) which are now universally applied. As far as dose specification for reporting is concerned, ICRU recommendations for photons (ICRU Report 50, 1993) can be extended and adapted for fast neutrons. However, special care is required to take into account the tissue compositions. In fast neutron therapy, specification of radiation quality raises a particular problem because the neutron RBE, relative to gamma rays, is higher than unity (it ranges from about 2 to 5) and furthermore significantly varies with neutron beam energy. In addition, the RBE also varies with dose and biological system. In these conditions, besides the classical concept of RBE introduced jointly by the ICRP and the ICRU in 1963, the concepts of "reference RBE" and "clinical RBE" are proposed here for application in fast neutron therapy. Microdosimetry provides an adequate method to describe radiation quality, at the point of interest in the irradiated medium and in the actual irradiation conditions. From the analysis of microdosimetric spectra, a RBE value of a particular neutron beam, for a given biological system, can be predicted provided that the biological weighing function for that biological system has been obtained. In any case, correlation of the microdosimetric description of a given beam and the experimental RBE values for that beam improves the confidence in both sets of data.
基于放射生物学依据，快中子于20世纪70年代被引入癌症治疗领域。30年后，这些依据依然有效，且未被最新实验数据推翻。尽管中子治疗已常规应用约25年，但对于其价值以及在其他放射治疗技术中的地位，仍未达成普遍共识。为了能够从现有的临床结果中得出客观结论，并且主要是以一种相关方式比较不同中心的结果，必须在几个问题上达成共识：1）在参考条件下均匀模体中剂量测量的方案；2）靶区和有风险正常组织层面的剂量计算；3）报告剂量规范的方法；4）中子治疗中辐射质量的规范以及相关的相对生物效应（RBE）问题。国际辐射单位与测量委员会（ICRU）已发布关于临床中子剂量学的建议（ICRU报告45，1989年），这些建议目前已被普遍应用。就报告剂量规范而言，ICRU关于光子的建议（ICRU报告50，1993年）可扩展并适用于快中子。然而，需要特别注意考虑组织成分。在快中子治疗中，辐射质量的规范引发了一个特殊问题，因为相对于伽马射线，中子的RBE高于1（范围约为2至5），而且还会随中子束能量显著变化。此外，RBE也随剂量和生物系统而变化。在这些情况下，除了ICRP和ICRU于1963年联合引入的经典RBE概念外，本文还提出了“参考RBE”和“临床RBE”概念，用于快中子治疗。微剂量学提供了一种合适的方法来描述在受照射介质中感兴趣点以及实际照射条件下的辐射质量。通过对微剂量学谱的分析，对于给定的生物系统，只要获得了该生物系统的生物权重函数，就可以预测特定中子束的RBE值。无论如何，给定束的微剂量学描述与该束的实验RBE值之间的相关性提高了对这两组数据的可信度。
